Một cây, nhiều dạng: tinh dầu, concrete, absolute và các dạng khác

ISO 9235 is the vocabulary standard for aromatic natural raw materials, prepared by ISO/TC 54 (Essential oils). The third edition was published in June 2021 and replaces the 2013 edition. According to its foreword, the two main changes are a revised definition at 3.13 (extract) and a new entry at 3.19 (native aromatic water). The document holds 31 terms in alphabetical order, with a thematic index and an alphabetical index.

The terms can be read in three layers. The first is raw materials: natural raw material, exudate, gum, oleoresin, balsam. The second is products of a primary process: essential oil, concrete, resinoid, pomade, supercritical fluid extract, absolute, aromatic water. The third is products of further treatment: rectified essential oil, terpeneless oils, concentrated (folded) essential oil, post-treated essential oil. This three-layer reading is the library's, not ISO's.

The key point: extract is the generic word for anything made with a solvent. A concrete is an extract from fresh material; a resinoid is an extract from dry material. An absolute is the ethanol-washed product of a concrete, a pomade, a resinoid or a supercritical fluid extract. Essential oil covers only three routes: steam distillation, mechanical pressing of citrus peel, and dry distillation. In ISO terms, absolutes and CO2 extracts are not essential oils.

Two of the library's forms have no entry of their own in ISO 9235:2021. The closest term to tincture is non-concentrated extract, an extract in which the solvent is kept, with benzoin in ethanol as the example. An isolate is a single compound separated from a natural material; the standard does not define it.

ISO definitions on this page are paraphrased. The original text is ISO copyright.

Distillation uses heat and water. Only molecules that can travel with steam reach the condenser. Waxes, pigments, sugars and most heavy molecules stay in the still. Heat and water can also change some compounds during the run.

Mechanical pressing applies only to citrus peel. There is no significant heat, so the non-volatile part of the oil glands, such as waxes, pigments and furocoumarins, comes along with the oil. This is why expressed and distilled bergamot oils are regulated differently.

Solvents (hexane, ethanol, CO2, or fat in enfleurage) dissolve heavy molecules and heat-sensitive ones. The product is often closer to the smell of the fresh material, but it carries waxes and may hold traces of solvent. After these three families come the secondary treatments: fractional distillation, rectification, deterpenation and isolation.

Yields in the table are product mass over raw material mass, taken from sourced examples. They vary with cultivar, season, freshness and equipment, so they indicate order of magnitude only. For absolutes the yield runs through two steps: flower to concrete, then concrete to absolute. For tinctures and pomades the solvent or fat is kept, so yield does not apply.

The solvent residue column names the solvent that may remain as traces, not a measured value. The volatility column describes the physical form at room temperature and which part of the product is volatile.

On trade labels the form usually sits inside the name: rose absolute, jasmine concrete, benzoin resinoid, ginger CO2, bergamot FCF, lemon terpeneless, ylang ylang extra.

On INCI cosmetic ingredient lists the form shows in the suffix. Distilled or expressed oils usually end in Oil, as in Flower Oil or Peel Oil. Solvent products, including absolutes and concretes, usually end in Extract. Hydrosols end in Water. So "Rosa Damascena Flower Oil" and "Rosa Damascena Flower Extract" are two different materials.

The form also decides which safety rules apply. Expressed bergamot oil contains bergapten and falls under an IFRA limit; bergamot FCF has had most furocoumarins removed. Crude birch tar and cade oils are excluded from fragrance use by IFRA; only rectified grades meeting the PAH limit may be used. Details sit on each form's page.